The field of the disclosure relates generally to methods and systems for inspecting gas well integrity, and more specifically to methods and systems for inspecting gas well integrity using a neutron and X-ray based inspection system.
In recent years, innovative production techniques have allowed access to oil and gas reserves previously considered inaccessible. Protecting the surrounding environment and assuring the long-term integrity of such wells are critical tasks for the oil and gas industry. Significant effort is devoted by the industry toward ensuring a safe and long operational life for all components of the oil and gas production and delivery infrastructure. Material degradation, defects on the installed tubular systems, shifts of ground formations, and other factors could lead to gas leakage, ground contamination, and potentially catastrophic consequences. Periodic, accurate, and complete inspections of the existing production infrastructure are an essential component of modern oil and gas industry maintenance strategy, addressing both operational safety, as well as water and ecosystem sustainability concerns. These concerns are of extreme relevance to communities located in areas of shale gas development, as well as for the nation as a whole.
The ability to inspect casings outside the innermost production casing in gas wells is a major issue for the industry. No technology currently exists that is capable of ‘seeing’ through inner casings in order to establish the integrity of the equipment outside of the wellbore. In particular, a major technology gap exists in so far as measuring the integrity of multiple well casing and cement annuli at intermediate-to-surface depths along major aquifers and ground water zones, where cracks, corrosion, and disbonding occur.
Known acoustic imaging technology with cement bond logs and variable density logs (CBL/VDL) is able to evaluate a single walled structure consisting of a single casing with bonded cement. However, this known acoustic imaging technology is not capable of inspecting multiple annuli in an intermediate zone where there are 2 to 5 stacked casing/cement rings. Furthermore, ultrasound-based techniques do not traditionally operate in gas filled wellbores and rely on using the drilling mud as a couplant for higher frequency sound for improved resolution.
Known electromagnetic inspection tools are sensitive only to the damages in metallic structures. Magnetic Flux Leakage (MFL) uses pipe wall magnetic saturation and magnetic sensors to detect variations in local magnetic field due to cracks and pit corrosion. However, systems that use MFL for crack detection can be used to inspect only the innermost wellbore pipe. Furthermore, eddy current tools rely on measuring the excitation of metallic components with an alternating electromagnetic field, which depends strongly on pipe electrical and magnetic properties and the cross-sectional area of the conductive material. However, eddy current sensors suffer from local variations in magnetic permeability that reduce the signal-to-noise ratio and require larger sensors. As a result, eddy current sensors have low spatial resolution.